JDK 9 RFR of JDK-8072480: javac should support compilation for a specific platform version

Magnus Ihse Bursie magnus.ihse.bursie at oracle.com
Mon May 25 07:51:20 UTC 2015

On 2015-05-22 14:38, Jan Lahoda wrote:
> Hi,
> I've uploaded a new iteration of the patch(es):
> top-level repository:
> http://cr.openjdk.java.net/~jlahoda/8072480/webrev.01/top-level/
> langtools:
> http://cr.openjdk.java.net/~jlahoda/8072480/webrev.01/langtools/
> (besides full webrevs, there are also webrevs showing the differences 
> between .00 and .01 available - see the "Delta webrev" link under 
> "Author's comments")
> Summary of changes:
> -applied Eric's build changes
> -moved CreateSymbols into make/src/classes/build/tools/symbolgenerator
> -tried to improve the specification of base platforms in 
> CreateSymbols, per Maurizio's comment
> -other cleanup in langtools per Maurizio's comments.

Looks good to me!

Copyright year in CreateSymbols.java says 2014, maybe time to update it? :-)


> Thanks,
>     Jan
> On 21.5.2015 12:31, Maurizio Cimadamore wrote:
>> Hi Jan,
>> great work - couple of comments below:
>> * it seems like some of the routines in Arguments can be simplified
>> using lambdas - especially lookupPlatformProvider and checkOptionAllowed
>> * Why JDKPlatformProvider is not called JDKPlatformProvider*Factory* ?
>> * JavacProcessingEnvironment.JoiningIterator seems to have commonalities
>> with CompoundScopeIterator - any chance that we might refactor this a 
>> bit?
>> * What's the rationale for giving an error if -platform is specified and
>> a non-StandardFileManager is provided? Can't we simply swallow that,
>> ignore the platform settings and issue a Lint 'options' warning?
>> * Would it make sense for some of the classfile generation logic in
>> CreateSymbols to be moved under the classfile API ?
>> * I had hard time reconciling some of the comments in CreateSymbols with
>> how the files were laid out. I think in the end, what you mean is that
>> if you have platforms 7, 8, 9 - you should pick one baseline (i.e. 8)
>> and then generate diffs for 9 and 7 against the 8 one. If that's the use
>> case, I think the command line can be simplified a bit in order to
>> explicitly state which of the platform is the baseline one, and the
>> remaining parameters can be inferred from the tool (as the
>> <base-platform-for-platform1,2 ... N> seem to be typically all identical
>> but one which is set to <none> - the one for the baseline). Maybe the
>> inference logic should be different (i.e. use 8 as a baseline for 7 and
>> 7 as a baseline for 6) - but - whatever the logic, I think it should be
>> chosen once and for all, and live implicitly in the tool? Or are there
>> reasons as to why it might be handy to customize the baselines?
>> Maurizio
>> On 21/05/15 08:01, Jan Lahoda wrote:
>>> Hi,
>>> This is a patch adding a new option, -platform, to javac.
>>> Patch for the top-level repository is here:
>>> http://cr.openjdk.java.net/~jlahoda/8072480/webrev.00/top-level/
>>> Patch for the langtools repository is here:
>>> http://cr.openjdk.java.net/~jlahoda/8072480/webrev.00/langtools/
>>> These changes also require additional langtools changes as their
>>> prerequisite:
>>> http://cr.openjdk.java.net/~jlahoda/8080675/webrev.00/
>>> Overall, one can imagine '-platform N' to have the same effect as
>>> '-source N -target N -bootclasspath <APIs-for-N>'. The possible values
>>> for 'N' are pluggable in a limited way, though (see
>>> langtools/src/jdk.compiler/share/classes/com/sun/tools/javac/platform/PlatformProvider.java). 
>>> Note that this patch only introduces N=7 and N=8, which correspond to
>>> Open JDK 7 and 8 GA.
>>> A tricky problem to solve is where to get the APIs for platform N. The
>>> proposal is to include history data in the textual format inside the
>>> OpenJDK repositories (the input data), process them at build time and
>>> create a lib/ct.sym file holding the data in the JDK image. javac
>>> running with the -platform option then compiles against the lib/ct.sym
>>> file. The input history data are placed
>>> <top-level-repository>/make/data/symbols (the sym.txt files). This
>>> patches only includes data for OpenJDK 7 and 8, and only for public
>>> APIs (more or less Java SE and JDK @Exported APIs).
>>> The size of the history data is currently ~6MB in the JDK checkout and
>>> ~650kB inside the .hg directory (the size could change significantly
>>> if additional classes/elements, like non-public API classes, would
>>> need to be included). The lib/ct.sym file is currently ~4.5MB.
>>> The ct.sym file is a zip file containing signature files. The
>>> signature files are similar to classfiles (so javac can read them as
>>> classfiles), but are missing some attributes, most notably the Code
>>> attribute. On the top-level, the ct.sym contains directories named
>>> "7", "78" and "8". When compiling for version 'N', the bootclasspath
>>> for that version is obtained by using directories which have 'N' in
>>> their name.
>>> The sigfiles for ct.sym are created by
>>> <top-level-repository>/make/tools/symbolgenerator/CreateSymbols.java.
>>> The same file can also be used to construct the sym.txt files. Concise
>>> instructions are part of the CreateSymbols.java.
>>> I am sending this as one review, as the changes together make one
>>> feature, but the langtools and top-level changes are independent to a
>>> great degree: the langtools changes add the "-platform" javac; and the
>>> top-level changes add the history data and ability to build the ct.sym
>>> file. If desired, these could be pushed and/or reviewed independently.
>>> Many thanks go to Jon Gibbons, Joe Darcy, Magnus Ihse Bursie, Alan
>>> Bateman and others who have provided advices and help on the matter
>>> before.
>>> Any insights/comments are wholeheartedly welcome.
>>> Thanks,
>>>     Jan

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